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Abstract:

Fragmentation of forest habitats can have a negative impact on the diversity of many species. When fragmentation impacts pollination, it can result in major changes to the composition of forest plant communities as well as a reduction in fruit production for nearby agriculture. I studied Hymenoptera diversity in a four hectare fragment and a continuous forest using Euglossine traps as well as a mixture of honey and water to attract Hymenoptera species. Hymenoptera diversity did not differ significantly between the two habitats but abundance of Hymenoptera, Euglossine, and Apidae were all significantly greater in the continuous forest site. This indicates that continuous forest supports a larger, more stable population of Hymenoptera species, thereby supplying steadier pollination services to the forest and nearby farms. ( ,, )

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2 and insolation are stronger in fragments, putting organisms at a greater risk for desiccation Aizen and Feinsinger 1994a. Consequently, susceptible species will suffer in fragments, potentially reducing diversity and abundance in these harsher habitats. Studies of different species have shown that many species suffe r when their forest habitat is fragmented Powell and Powell 1987, Aizen and Feinsinger 1994a. For example, a study by Sekercioglu et al. 2001 found significantly fewer insectivorous birds in the understory of fragments compared to continuous forests. They reported that the best determinant of success by a bird species in fragments was the ability to disperse through deforested habitats Sekercioglu et al. 2001. By changing the conditions of the habitat, fragments can add new selective pressures for species, favoring those that can adapt to the new conditions. Changes in species composition have a stronger impact on the forest when they disrupt pollination and seed dispersal mutualisms Aizen and Feinsinger 1994a. When pollinator populations change , this can impact both native plant species and nearby crops Aizen and Feinsinger 1994b because diversity of pollinators may impact pollination and consequently seed and fruit set Ricketts 2003. A study by Ricketts et al. 2004 showed that coffee pla nts near large forest patches greater than 46 ha produced more fruit than those located far from forest. Pollination studies showed that the increase in production was due to the pollination services received from the nearby forest Ricketts et al. 2004 . However, it is still unclear if small fragments will yield the same benefit. This study addresses the effects of fragmentation on the abundance and diversity of Hymenoptera. Hymenopterans have a large impact on the forest community because they provi de pollination services through bees Apidae and biological control of agricultural pests through wasps Kean and Barlow 2001. My purpose was to determine how fragmentation impacts Hymenoptera populations. My hypothesis was that Hymenoptera diversity an d abundance would differ between the four hectare fragment and the continuous forest. I predicted that diversity and abundance would be greater in the continuous forest. The results of my study will provide insight into what land use strategies are necess ary to preserve forest Hymenoptera species for conservation and agricultural benefits. MATERIALS AND METHODS My two study sites were located in San Luis, a farming community in Puntarenas, Costa Rica. The farms in San Luis are bordered by either con tinuous forest or forest fragments. The continuous forest site was located near the e d g e of a forest that is contiguous with the Monteverde Cloud Forest Preserve. The fragment site, located less than one km away from the continuous forest, was a four hec tare patch situated behind a series of small coffee farms collectively known as Finca la Bella. In each site, I placed my traps 100 m in from the edge of the forest. To catch Euglossine bees, I hung two commercial, yellow euglossine bee traps in each sit e. The traps were hung from branches at eye level 1.5 m and were located roughly two meters apart. I placed blotter paper covered with eugenol scent inside each trap. I visited each site in the morning for 11 days between October 26 and November 15. Each day I took three samples of the number of bees present inside or outside the trap. I recorded the bees present when I arrived, ten minutes later, and again

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3 after another ten minutes. I preserved a sample of each species in a vial of alcohol and late r identified the species to the genus level. To study overall Hymenoptera diversity and abundance, I visited each site six times in the morning from November 8 to November 15. In each site, I selected two palm branches at eye level 1.5 m roughly three meters apart. I sprayed the underside and topside of the leaves with a mixture of one part honey to four parts water. Ten minutes later, I observed each branch for one minute and recorded the number of each Hymenoptera species present. I repeated this two more times for a total of three observations per site each day. I used the Shannon Weiner diversity index to calculate the Shannon Weiner diversity indices for the continuous forest and the fragment. I then used a t test to determine if the indices were significantly different. I used three separate chi squared tests to compare the abundances of Hymenoptera, bees, and Euglossine bees in the continuous and fragment sites. RESULTS I observed nine species in the continuous forest site and found al l but two of the same species in the fragment site Fig 1. Apis mellifera and the clear wing morphospecies were not found in the fragment site Fig 1. No species were found only in the fragment and all except two species were observed more often in the continuous site Fig 1. Eulaema sp. was observed only once in each habitat Fig 1. The yellow morphospecies of Ichneumonidae was the only species that was more abundant in the fragment site with ten sightings in the fragment and seven in the continuou s site Fig 1. Hymenoptera diversity was not significantly different between continuous forest H = 0.659 and fragmented forest habitats H = 0.631 t test, t = 0.343, df = 94.31, p>.05, Fig 1. Hymenoptera abundance was significantly greater in con tinuous forest compared to the fragment Ã°c 2 = 100.77, df =1, p
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4 Euglossine that I found in the continuous site. These results indicate that fragmentation may lead to smaller populations of Hymenoptera species. Due to genetic drift, a reduced population size is likely to lead to reduced genetic variability, which in turn leads to less stable populations with a greater likelihood of extinction Aizen and Feinsinger 1994a. Some of the observed Hymenoptera species may later experience local ext inctions in this fragment due to their decreased abundance. This would reduce the local diversity of Hymenopterans in the fragment. In the future, the continuous forest may contain greater Hymenoptera diversity, especially if further fragmentation of the four hectare patch occurs. It remains to be seen whether fragmentation will ultimately lead to a decrease in Hymenoptera diversity. However, we do know that as conditions change with fragmentation, species that do well in disturbed areas, such as me mbers of the Ichneumonidae family and Apis mellifera Gauld 1995 and Hanson et al.1995, will have an advantage over species that suffer in fragments, such as Euglossians Powell and Powell 1987. This is not only true for Hymenoptera species; as an order with many plant animal interactions, a change in either Hymenoptera abundance, diversity, or composition is likely to mean changes for plant communities as well Aizen and Feinsinger 1994b. Plants that are dependent on declining pollinator species will suffer declines themselves. Euglossine bees are significant pollinators for over 30 tropical plant families including Orchidaceae, Solanaceae, Bignoniaceae, and Luguminaceae. If euglossine bee populations decline in fragmented forest, as it seems they ha ve done in San Luis, these plant families are likely to follow Powell and Powell 1987. It is likely that this change in pollinator composition will ultimately result in a less diverse community of plants. Aizen and Feisinger s study on forest fragment ation revealed that 13 out of the 16 plant species studied showed declines in pollination levels from continuous forest to fragments. Seed production also decreased for many of these species in the fragmented forest patches as a result of reduced pollinat ion. This suggests that a smaller group of species will contribute more seeds to the seed set. These few species will eventually come to dominate the plant community in fragments Aizen and Feinsinger 1994a. In a farming community like San Luis, preserv ation of forest diversity is not just for conservation s sake alone. The pollination services provided by forest bee species are highly valuable to nearby agricultural production Ricketts et al 2004. More diverse pollinator populations stabilize pollina tion services and help buffer against declines in any one species Ricketts 2004. Taylor Ricketts has shown that coffee farms near large patches of forest 46 and 111 ha produce more and higher quality coffee than farms near a narrow riparian strip 2.5 km long by 30 70 m wideRickets 2004. In addition, many species of wasps can also provide ecosystem services as biological control agents for agricultural pests Kean and Barlow 2001. The results of my study demonstrate that small forest fragments, ev en within one km of continuous forest, cannot support the same size of Hymenoptera populations that continuous forest can. This indicates that communities like San Luis cannot continue to fragment their surrounding forests to produce more land for agricul ture. As a result, farmers may lose money in the end due to decreased crop yield following decreased pollinator abundance. Further directions for research include repeating this study with a